Multiple DNA repair pathways have evolved to maintain genomic integrity in the face of a constant barrage of genotoxic agents. Defects in various DNA repair mechanisms result in a strong predisposition to cancer. In addition to DNA repair pathways, the replication checkpoint plays an important role. In response to S-phase insults, the replication checkpoint maintains genomic stability by coordinating cellular responses such as; cell-cycle arrest, fork stabilization and DNA repair. Cancer risk is elevated by mutations in human proteins that are required for the replication checkpoint. This proposal is aimed at exploring the important interface between DNA repair and the replication checkpoint, about which little is known. These studies will employ the fission yeast, Schizosaccharomyces pombe, which has proven invaluable in the analysis of DNA repair and checkpoint pathways that are conserved in humans. The DNA repair protein Rad60 interacts with the replication checkpoint kinase, Cdsl. Rad60 is part of the essential Smc5-Smc6 complex that is required for DNA repair and genomic integrity. Rad60 is subject to Cdsl-dependent regulation and therefore, the first aim is to uncouple Cdsl-Rad60 communication and study the effects on genomic stability. The second aim focusses on understanding the function of Rad60, which in turn should reveal an important mechanism through which Cdsl maintains the genome. The third aim is to explore the function of the Smc5-Smc6 complex, of which Rad60 is a part. The Smc5-Smc6 complex likely plays a role in chromosome structure and thereby facilitates DNA repair. Little is known about the role of chromatin structure in DNA repair and therefore these studies will help elucidate this connection. Results obtained in this study will likely prime analogous studies of the human homologues of the above proteins, resulting in a better understanding of the interface between the replication checkpoint and DNA repair in humans.